The present invention relates generally to semiconductor wafer vacuum processing systems and to single wafer, cassette-to-cassette, robot vacuum processing systems.
In order to decrease contamination and to enhance through-put, a number of recently introduced, single-wafer processing chambers use a system configuration comprising a wafer transfer robot which transports wafers between a cassette load lock and plural/multiple vacuum processing chambers. Access (1) between the individual process chambers and (2) between the robot chamber and the load lock chamber is via slit valves which selectively isolate the process chambers from the robot and the robot from the load lock chamber. This configuration permits processing in one or more chambers while wafers are being loaded or unloaded at other process chambers or at the load lock chamber and permits random access, in vacuo wafer transfer from one processing chamber to another via the robot chamber.
An article entitled "Dry Etching Systems: Gearing Up for Larger Wafers", in the October, 1985 issue of Semiconductor International magazine, pages 48-60, discloses such a system and specifically, a four-chamber dry etching system in which a robot in a pentagonal-shaped housing serves four plasma etching chambers and a cassette load/unload load lock chamber mounted on the robot housing.
Despite the increased vacuum isolation provided by such state-of-the-art systems, to our knowledge typically such systems have difficulty providing commercially acceptable throughput for high vacuum processes, for example, physical vapor processes such as sputtering. Specifically, the time required to pump down processing chambers or their load lock chambers to their base level, following loading of wafers into the chambers, is excessive.